The entire disclosures of Japanese Patent Application Nos. 2008-020356, filed Jan. 31, 2008, 2008-116677, filed Apr. 28, 2008, are expressly incorporated herein by reference.
1. Technical Field
The present invention relates to a liquid ejecting head, such as an ink jet recording head, and a liquid ejecting apparatus. More specifically, the present invention relates to a liquid ejecting head having an improved ability to discharge air bubbles in the liquid ejecting head, and a liquid ejecting apparatus having the same.
2. Related Art
Examples of liquid ejecting heads currently known in the art that eject or discharge liquid from a nozzle orifice by fluctuating the pressure of the liquid in a pressure chamber include, for example, an ink jet recording head (hereinafter referred to as a recording head) used in an image recording apparatus such as an ink jet recording apparatus (hereinafter referred to as printer), a color material ejecting head used for manufacturing color filters of liquid crystal displays or the like, an electrode material ejecting head used for forming electrodes of organic EL (electroluminescence) displays, FEDs or field emission displays, or the like, and a bioorganic matter ejecting head used for manufacturing biochips (biochemical elements).
The above recording head is made by laminating a plurality of components. For example, a recording head disclosed in Japanese Patent Application No. JP-A-11-277743 includes an actuator unit serving as a pressure generator, a pressure chamber unit that forms a plurality of pressure chambers, and a passage unit that forms a plurality of liquid passages. The actuator unit and pressure chamber unit, and passage unit are then laminated and integrated.
The pressure chamber unit is made by laminating a pressure chamber plate or spacer having a plurality of pressure generating chambers formed therein, a communication port plate or second cover having nozzle communication ports and supply side communication ports formed therein, and a vibrating plate or first cover on which piezoelectric vibrators are mounted. The components are then integrated into a single component using a process such as, for example, firing. The passage unit is made by laminating a number of plate members, including a supply port plate or ink supply port forming substrate having supply ports formed therein, a reservoir forming substrate having reservoirs or common liquid chambers formed therein, and a nozzle plate in which a plurality of nozzle orifices are arranged in lines in order to form rows of nozzles. The plate members are then bonded together with adhesive so as to integrate them into a single component. When ink is ejected by the recording head, a pressure chamber is preliminarily expanded before ink is ejected, creating a vacuum. This causes the ink to be supplied from the corresponding reservoir via the corresponding supply port to the pressure chamber. Then, by rapidly contracting the pressure chamber after the preliminary expansion, ink is ejected from the corresponding nozzle orifice.
In the recording head having the above structure, it is most preferable that the ink passages inside the recording head be filled with ink. However, air can enter the ink passages when ink is initially filled in the recording head or when the ink cartridge is replaced. Moreover, outside air can pass through the walls of the recording head and generate air bubbles in the ink passages. It is difficult to completely prevent this. Once formed inside the ink passages, the air bubbles unite and produce larger bubbles. If such air bubbles stay in the ink passages, the air bubbles can absorb the pressure fluctuation at the time of the ejecting operation, causing a pressure loss. In addition, the air bubbles can block the passages, thereby causing an inadequate supply of ink to the recording head.
To prevent problems caused by air bubbles, various recovery operations are performed in the ink jet recording apparatus having the above recording head. For example, a cleaning operation may be performed to suck and discharge air bubbles and residual ink from the recording head through the nozzle orifices.
However, as shown in FIG. 5, when the adhesive A used to bond the plate members results in a recess in the inner wall surface of the ink passage 52, air bubbles B can form in the recess. Once air bubbles B enter this recess, it is difficult to remove the air bubbles, even when a cleaning operation is performed, so the above-described problems cannot be fixed. In contrast, when a larger amount of adhesive is used in the bonding process so that adhesive protrudes into the ink passage, the adhesive that extends into the ink passage can block any minute through-holes 53 such as the nozzle orifices and the supply ports.